The purpose of this project is to develop a reliable, rapid, convenient, and quantitative system for assay of malignant transformation and mutation in the cells of different species and origins in order to provide the optimum system for studying the mechanism of cell transformation as well as for obtaining the assay system for assessment of human risk against environmental carcinogens. This project may also lead to finding the crucial factors involved in the cell transformation. The skin fibroblasts derived from the patients with familial polyposis and Bloom's syndrome were examined for their behavior in culture to find no unique features compared to the normal skin fibroblasts. Further studies are in progress to determine whether the cells from these patients who are genetically predisposed to higher incidence of cancer are highly sensitive to the transformation as well as mutation. A protocol for quantitative and efficient system for assay of dominant mutation of human diploid fibroblasts was established using diphtheria-toxin resistance marker after extensive examination of experimental conditions. The factors contained in the serum which markedly affect the frequencies of chemically induced transformation are being investigated.